U.S. patent application number 10/958396 was filed with the patent office on 2005-03-03 for crystallization apparatus and crystallization method.
Invention is credited to Jyumonji, Masayuki, Kimura, Yoshinobu, Matsumura, Masakiyo, Nishitani, Mikihiko, Taniguchi, Yukio, Tsujikawa, Susumu, Yamaguchi, Hirotaka.
Application Number | 20050048383 10/958396 |
Document ID | / |
Family ID | 30112599 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050048383 |
Kind Code |
A1 |
Taniguchi, Yukio ; et
al. |
March 3, 2005 |
Crystallization apparatus and crystallization method
Abstract
A crystallization apparatus includes an illumination system
which illuminates a phase-shift mask and an image-forming optical
system arranged in an optical path between the phase-shift mask and
a semiconductor film. The semiconductor film is irradiated with a
light beam having a light intensity distribution of inverted peak
patterns whose light intensity is the lowest in portions
corresponding to phase shift sections to form a crystallized
semiconductor film. The image-forming optical system is located to
optically conjugate the phase-shift mask and the semiconductor film
and has an aberration corresponding to the given wavelength range
to form a light intensity distribution of inverted peak patterns
with no swell of intensity in the middle portion.
Inventors: |
Taniguchi, Yukio;
(Yokohama-shi, JP) ; Matsumura, Masakiyo;
(Yokohama-shi, JP) ; Yamaguchi, Hirotaka;
(Yokohama-shi, JP) ; Nishitani, Mikihiko;
(Yokohama-shi, JP) ; Tsujikawa, Susumu;
(Yokohama-shi, JP) ; Kimura, Yoshinobu;
(Yokohama-shi, JP) ; Jyumonji, Masayuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
30112599 |
Appl. No.: |
10/958396 |
Filed: |
October 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10958396 |
Oct 6, 2004 |
|
|
|
PCT/JP03/03367 |
Mar 19, 2003 |
|
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Current U.S.
Class: |
430/5 ;
250/492.22; 257/64; 257/E21.134; 257/E21.347; 257/E21.413;
257/E29.293 |
Current CPC
Class: |
Y10S 117/904 20130101;
H01L 21/02678 20130101; H01L 29/66757 20130101; H01L 21/02532
20130101; H01L 21/02488 20130101; B23K 26/066 20151001; Y10T
117/1008 20150115; H01L 29/78675 20130101; H01L 21/268 20130101;
H01L 21/02422 20130101; Y10S 117/905 20130101; Y10T 117/1004
20150115; Y10S 117/90 20130101; Y10T 117/10 20150115 |
Class at
Publication: |
430/005 ;
250/492.22; 257/064 |
International
Class: |
H01L 031/036; G21K
005/10; H01L 029/04; G03F 009/00; H01J 037/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2002 |
JP |
2002-202009 |
Claims
What is claimed is:
1. A crystallization apparatus comprising: a phase-shift mask
having at least two phase-shift sections; an illumination system
which emits a light beam of a given wavelength range to illuminate
the phase-shift mask; and an image-forming optical system arranged
in an optical path between the phase-shift mask and a subject to be
processed, the phase-shift mask converting an intensity pattern of
the light beam emitted from the illumination system so as to have a
light intensity distribution having inverted peak pattern portions
having a smallest peak value of light intensity in portions
corresponding to the phase-shift section, and applying the light
beam to the subject to crystallize the substrate, wherein the
phase-shift mask and the subject are arranged in a conjugate
position of the image-forming optical system, and the image-forming
optical system has an aberration corresponding to the given
wavelength range to form a light intensity distribution of waveform
patterns with no swell of intensity in a middle portion between the
inverted peak pattern portions on the subject.
2. The crystallization apparatus according to claim 1, wherein the
aberration corresponding to the given wavelength range is a
chromatic aberration that represents that optical components of
different wavelengths vary in image-forming positions almost in a
direction of an optical axis.
3. The crystallization apparatus according to claim 1, wherein the
illumination system has a light source which supplies a light beam
having a Gaussian wavelength-to-intensity distribution as a
whole.
4. The crystallization apparatus according to claim 1, wherein the
illumination system has a light source which supplies a light beam
having a maximum intensity at a plurality of given wavelengths that
differ from one another.
5. The crystallization apparatus according to claim 4, wherein the
given wavelengths are provided at almost regular intervals within
the given wavelength range.
6. The crystallization apparatus according to claim 4, wherein the
light source includes an etalon having an interval between
reflection planes corresponding to an interval between the given
wavelengths.
7. The crystallization apparatus according to claim 4, wherein the
light source has a plurality of light source sections which supply
light beams of central wavelengths that differ from one another in
accordance with the given wavelengths and a synthesizing section
which synthesizes a plurality of light beams supplied from the
light source sections.
8. The crystallization apparatus according to claim 2, wherein when
a maximum value of a longitudinal aberration caused due to the
aberration based on the light beam supplied from the light source
is D, a central wavelength of the light beam supplied from the
light source is .lambda., and a pitch between the inverted peak
pattern portions formed on the subject is X, a following expression
is satisfied:
0.87.ltoreq.D.multidot..lambda./X.sup.2.ltoreq.1.389.
9. The crystallization apparatus according to claim 2, wherein when
a central wavelength of the light beam supplied from the light
source is .lambda., a half width at half maximum of the intensity
distribution of the light beam supplied from the light source is
.DELTA..lambda., a coefficient indicating a ratio of an amount of
defocus to an amount of displacement of a wavelength from the
central wavelength .lambda. is k, and a pitch between the inverted
peak pattern portions formed on the subject is X, a following
expression is satisfied:
0.087.ltoreq.k.multidot..DELTA..lambda..multidot..lambda./X.sup.2.ltoreq.-
1.389.
10. A crystallization apparatus comprising: a light source which
emits a light beam of a given wavelength range; a phase-shift mask
having at least two phase-shift sections, and converting an
intensity pattern of the light beam emitted from the light source
so as to have a light intensity distribution having inverted peak
pattern portions whose light intensity is lowest at points
corresponding to the phase-shift sections and applying the light
beam to a subject to be processed to crystallize the substrate; and
an optical system for changing the light beam of the given
wavelength range such that the light beam applied to the subject
has a plurality of optical elements whose wavelengths are different
and forming a light intensity distribution of waveform patterns
with no swell of intensity in a middle portion between the inverted
peak pattern portions on the subject.
11. The crystallization apparatus according to claim 10, wherein
the optical system sets the light intensity distribution in
cooperation with the phase-shift mask such that a middle portion
between the waveform patterns has a mountain shape on the
subject.
12. The crystallization apparatus according to claim 10, wherein
the optical system includes optical member provided between the
light source and the phase-shift mask to change the light beam of
the given wavelength range, which is emitted form the light source,
so as to have a plurality of optical components whose wavelengths
are different and apply the light beam to the phase-shift mask.
13. The crystallization apparatus according to claim 9, wherein the
optical system includes optical member provided between the
phase-shift mask and the subject to change a light beam having
inverted peak pattern portions, which is emitted from the
phase-shift mask, so as to have a plurality of optical components
whose wavelengths are different and apply the light beam to the
subject.
14. A method of crystallizing a subject to be processed by
illuminating a phase-shift mask and irradiating the substrate with
a light beam having a light intensity distribution of inverted peak
pattern portions whose light intensity is lowest in portions
corresponding to at least two phase-shift sections of the
phase-shift mask, the method comprising: illuminating the
phase-shift mask with a light beam of a give wavelength range; and
forming a light intensity distribution, which has no swell of
intensity in a middle portion between the inverted peak pattern
portions, on the subject through an image-forming optical system,
the image-forming optical system being located to optically
conjugate the phase-shift mask and the subject and having an
aberration corresponding to the given wavelength range.
15. The method according to claim 14, wherein the middle portion
has an intensity distribution of a mountain shape.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation Application of PCT Application No.
PCT/JP03/03367, filed Mar. 19, 2003, which was published in
Japanese.
[0002] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2002-202009,
filed Jul. 11, 2002, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a crystallization apparatus
and a crystallization method. Specifically, the present invention
relates to an apparatus and a method for forming a crystallized
semiconductor film by irradiating a polycrystalline semiconductor
film or an amorphous semiconductor film with a laser beam whose
phase is modulated using a phase-shift mask.
[0005] 2. Description of the Related Art
[0006] Conventionally, the materials of a thin-film transistor
(TFT) used for, e.g., a switching element that controls a voltage
to be applied to pixels of a liquid crystal display (LCD) are
roughly divided into amorphous silicon and polysilicon. The
electron mobility of the polysilicon is higher than that of the
amorphous silicon. If, therefore, a transistor is formed by
polysilicon, its switching speed becomes higher than that of a
transistor formed by amorphous silicon, which brings about the
advantages that the response speed of a display can increase and
the design margins of other components can decrease. If, moreover,
peripheral circuits such as a driver circuit and a DAC as well as a
display main unit are incorporated into the display, they can be
operated at higher speed.
[0007] Though polysilicon is formed of a set of crystal gains, its
electron mobility is lower than that of image crystal silicon. A
small-sized transistor that is formed by polysilicon has a problem
of variations in the number of crystal grain boundaries in a
channel section. A crystallization method for generating
large-diameter image crystal silicon has recently been proposed in
order to improve the electron mobility and lessen the variations in
the number of crystal grain boundaries in a channel section.
[0008] As a crystallization method of this type, there has
conventionally been known phase control excimer laser annealing
(ELA) for forming a crystallized semiconductor film by applying an
excimer laser beam to a phase-shift mask that is parallel and close
to a polycrystalline semiconductor film or an amorphous
semiconductor film. The details of the phase control ELA are
disclosed in, for example, Surface Science, Vol. 21, No. 5, pp.
278-287, 2000. The same technology is also disclosed in Jpn. Pat.
Appln. KOKAI Publication No. 2000-306859 (KOKAI date: November
2).
[0009] The phase control ELA generates a light intensity
distribution of an inverted peak pattern in which the light
intensity of a portion corresponding to a phase-shift section of
the phase-shift mask is approximately zero (a pattern of light
intensity which is approximately zero in the center of the
phase-shift mask and suddenly increases toward the periphery
thereof). A polycrystalline semiconductor film or an amorphous
semiconductor film is irradiated with light having the light
intensity distribution of an inverted peak pattern. As a result, a
melting region is generated in accordance with the light intensity
distribution, and a crystal nucleus is formed in a portion unmelted
or solidified first in accordance with the portion whose light
intensity is approximately zero. Crystal grows laterally from the
crystal nucleus toward its periphery (lateral growth) to generate a
large-diameter single crystal.
[0010] As described above, prior art (proxy method) for forming a
crystallized semiconductor film by applying an excimer laser beam
to a phase-shift mask that is parallel and close to a semiconductor
film is known. However, the proxy method has a drawback in which
the phase-shift mask is contaminated due to abrasion of the
semiconductor film thereby to prevent good crystallization.
[0011] Applicant of the present application therefore proposes a
technology (image defocus method) of forming a crystallized
semiconductor film by defocusing a semiconductor film with respect
to an image-forming optical system that is interposed between a
phase-shift mask and a substrate to be processed (semiconductor
film). Applicant also proposes a technology (image NA method) of
arranging an image-forming optical system to optically conjugate a
phase-shift mask and a semiconductor film and forming a
crystallized semiconductor film by defining the numerical aperture
of the image-forming optical system on its laser beam emitting
side.
[0012] According to the above image defocus method and image NA
method, generally, a KrF excimer laser light source that outputs a
KrF excimer laser beam of a high output is employed and so is an
image-forming optical system that is made of a single type of
optical material (e.g., silica glass). In this case, the
oscillation wavelength band of the KrF excimer laser beam is
relatively broad (about 0.3 nm at full width at half maximum: see
FIG. 5), and the image-forming optical system causes a relatively
large chromatic aberration. Consequently, an influence of the
broadband wavelength of the KrF excimer laser beam and the
chromatic aberration of the image-forming optical system can
prevent a required light intensity distribution from being
generated on a substrate to be processed, such as a semiconductor
film. In order to generate a required light intensity distribution
on a semiconductor film, it can be thought that the waveband of a
laser beam is narrowed using a prism, a diffraction grating or the
like. If, however, the waveband of a laser beam is narrowed, a
laser unit will be increased in size and complicated and its output
will be lowered.
[0013] Using a laser beam whose waveband is narrow, generally, the
light intensity distribution in a middle portion M between adjacent
two inverted peak pattern portions R is accompanied by an irregular
swell (see FIG. 4). In the crystallization process, a crystal
nucleus is sometimes formed in a position of the swell of the
middle portion M where the light intensity is low (or in an
undesired position). Even though a crystal nucleus is formed in a
desired position, the lateral growth, which starts from the crystal
nucleus toward the periphery thereof, stops in a position of the
middle portion M where the light intensity decreases. It is thus
likely that a large crystal will be prevented from growing.
[0014] An object of the present invention is to provide a
crystallization apparatus and a crystallization method capable of
forming a crystal nucleus in a desired position and allowing a
crystal to grow in a fully lateral direction from the crystal
nucleus to thereby generate a large-diameter crystal grain.
BRIEF SUMMARY OF THE INVENTION
[0015] To solve the problem, according to a first aspect of the
present invention, there is provided a crystallization apparatus
comprising:
[0016] a phase-shift mask having at least two phase-shift
sections;
[0017] an illumination system which emits a light beam of a given
wavelength range to illuminate the phase-shift mask; and
[0018] an image-forming optical system arranged in an optical path
between the phase-shift mask and a subject to be processed, the
phase-shift mask converting an intensity pattern of the light beam
emitted from the illumination system so as to have a light
intensity distribution having inverted peak pattern portions having
a smallest peak value of light intensity in portions corresponding
to the phase-shift section, and applying the light beam to the
subject to crystallize the substrate,
[0019] wherein the phase-shift mask and the subject are arranged in
a conjugate position of the image-forming optical system, and
[0020] the image-forming optical system has an aberration
corresponding to the given wavelength range to form a light
intensity distribution of waveform patterns with no swell of
intensity in a middle portion between the inverted peak pattern
portions on the subject.
[0021] According to a second aspect of the present invention, there
is provided a crystallization apparatus comprising:
[0022] a light source which emits a light beam of a given
wavelength range;
[0023] a phase-shift mask having at least two phase-shift sections,
and converting an intensity pattern of the light beam emitted from
the light source so as to have a light intensity distribution
having inverted peak pattern portions whose light intensity is
lowest at points corresponding to the phase-shift sections and
applying the light beam to a subject to be processed to crystallize
the substrate; and
[0024] means for changing the light beam of the given wavelength
range such that the light beam applied to the subject has a
plurality of optical elements whose wavelengths are different and
forming a light intensity distribution of waveform patterns with no
swell of intensity in a middle portion between the inverted peak
pattern portions on the subject.
[0025] According to a third aspect of the present invention, there
is provided a method of crystallizing a subject to be processed by
illuminating a phase-shift mask and irradiating the substrate with
a light beam having a light intensity distribution of inverted peak
pattern portions whose light intensity is lowest in portions
corresponding to at least two phase-shift sections of the
phase-shift mask, the method comprising:
[0026] illuminating the phase-shift mask with a light beam of a
give wavelength range; and
[0027] forming a light intensity distribution, which has no swell
of intensity in a middle portion between the inverted peak pattern
portions, on the subject through an image-forming optical system,
the image-forming optical system being located to optically
conjugate the phase-shift mask and the subject and having an
aberration corresponding to the given wavelength range.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0028] FIG. 1 is a schematic view showing a configuration of a
crystallization apparatus according to an embodiment of the present
invention.
[0029] FIG. 2 is a schematic view of the internal structure of an
illumination system shown in FIG. 1.
[0030] FIGS. 3A and 3B are a plan view and a side view each showing
a phase-shift mask used in the crystallization apparatus.
[0031] FIG. 4 is a graph showing a light intensity distribution of
inverted peak pattern portions formed by an image defocus method
and an image NA method.
[0032] FIG. 5 is a graph showing an oscillation wavelength
distribution of a KrF excimer laser light source in an example of
numeric values according to the embodiment of the present
invention.
[0033] FIGS. 6A and 6B are illustrations of an influence of a
chromatic aberration of an image-forming optical system in the
embodiment of the present invention.
[0034] FIG. 7 is a graph showing light intensity patterns formed on
a substrate to be processed by optical elements of respective
wavelengths in the example of numeric values according to the
embodiment of the present invention.
[0035] FIG. 8 is a graph showing a light intensity distribution
formed finally on the substrate to be processed in the example of
numeric values according to the embodiment of the present
invention.
[0036] FIGS. 9A and 9B are illustrations of the structure and
function of an etalon that converts a broadband laser beam into
optical elements of different wavelengths in different
modifications to the embodiment of the present invention.
[0037] FIGS. 10A and 10B are charts of an oscillation wavelength
distribution of a light source and point images formed by a
plurality of wavelength light beams.
[0038] FIG. 11 is a graph showing light intensity patterns formed
on a substrate to be processed by optical elements of different
wavelengths in the modifications to the embodiment of the present
invention.
[0039] FIG. 12 is a graph showing a light intensity distribution
formed finally on a substrate to be processed in the modifications
to the embodiment of the present invention.
[0040] FIGS. 13A to 13E are sectional views of steps of
manufacturing an electronic device using the crystallization
apparatus according to the embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0041] An embodiment of the present invention will be described
with reference to the accompanying drawings.
[0042] FIG. 1 is a schematic view showing a configuration of a
crystallization apparatus according to the embodiment of the
present invention, and FIG. 2 is a schematic view of the internal
structure of an illumination system shown in FIG. 1. Referring to
FIGS. 1 and 2, the crystallization apparatus of the present
embodiment includes an illumination system 2 that illuminates a
phase-shift mask 1. The illumination system 2 has a KrF excimer
laser light source 2a that supplies a laser beam having a
wavelength of 248 nm, a beam expander 2b arranged in sequence on
the laser beam emitting side of the light source, a first fly-eye
lens 2c, a first condenser optical system 2d, a second fly-eye lens
2e and a second condenser optical system 2f.
[0043] The laser beam supplied from the light source 2a expands
into one having a given diameter through the beam expander 2b and
then enters the first fly-eye lens 2c. Thus, a plurality of small
light sources are formed on the rear focal plane of the first
fly-eye lens 2c, and light fluxes of beams from the small light
sources illuminate the incident plane of the second fly-eye lens 2e
in a superimposed fashion through the first condenser optical
system 2d. As a result, a plurality of small light sources the
number more than the small light sources on the rear focal plane of
the first fly-eye lens 2c are formed on the rear focal plane of the
second fly-eye lens 2e. Beam fluxes from the small light sources
illuminate the phase-shift mask 1 in a superimposed fashion through
the second condenser optical system 2f.
[0044] The first fly-eye lens 2c and the first condenser optical
system 2d make up a first homogenizer, and the first homogenizer
uniforms the intensity with respect to the angle of incidence on
the phase-shift mask 1. The second fly-eye lens 2e and the second
condenser optical system 2f make up a second homogenizer, and the
second homogenizer uniforms the intensity with respect to an
in-plane position on the phase-shift mask. Thus, the illumination
system applies a laser beam having an almost uniform light
intensity distribution to the phase-shift mask 1.
[0045] A laser beam whose phase is modulated by the phase-shift
mask 1 is applied to a substrate 4 to be processed through an
image-forming optical system 3. The phase-shift mask 1 and the
substrate 4 are located in an optically conjugate position of the
image-forming optical system 3. The substrate 4 is obtained by
sequentially forming an underlying film and an amorphous silicon
film on a plate glass for liquid crystal displays by chemical vapor
deposition. The substrate 4 is held in a given position on a
substrate stage 5 by a vacuum chuck, an electrostatic chuck or the
like. The substrate stage can be moved in X, Y and Z directions by
a drive mechanism not shown.
[0046] FIGS. 3A and 3B are schematic views showing a structure of a
phase-shift mask. Generally speaking, as described in the foregoing
prior art, the phase-shift mask is made of a transparent medium,
e.g., a quartz substrate having adjacent regions that vary in
thickness. In a boundary of a step (phase-shift section) between
the adjacent regions, the phase-shift mask diffracts the incident
laser beam fluxes and makes them interfere with each other and
provides the intensity of the incident laser beam with a
periodical, spatial distribution.
[0047] More specifically, with reference to FIG. 3A, the
phase-shift mask 1 has slit-shaped phase regions 1a and 1b of two
types, which are alternately arranged in one direction (horizontal
direction in FIG. 3A). The first phase region 1a and the second
phase region 1b are formed to make a phase difference of
180.degree. between their transmitted laser beam fluxes. If the
phase-shift mask 1 is formed of silica glass having a refractive
index of 1.5 with respect to a laser beam whose wavelength is 248
nm, a step of 248 nm is formed between the first phase region 1a
and the second phase region 1b, as is understood from FIG. 3B. In
other words, there is a 248 nm difference in thickness between both
the regions 1a and 1b. A boundary between the first phase region 1a
and the second phase region 1b corresponds to a phase-shift section
1c.
[0048] If an image defocus method (or an image NA method) is
applied to an optical system whose light source supplies a
single-wavelength or narrow-band laser beam and whose image-forming
optical system has almost no aberration, the substrate 4 is located
in a defocus position of an image-forming optical section (or the
numerical aperture of the image-forming optical system on its laser
beam emitting side is defined), with the result that a laser beam
having a light intensity distribution of an inverted peak pattern
corresponding to the phase of the phase-shift mask 1 is applied
onto the substrate 4, as illustrated in FIG. 4. The light intensity
distribution has the following characteristics. The light intensity
is a minimum inverted peak value of approximately zero in a
position corresponding to each of phase-shift sections 1c of the
phase-shift mask 1, and increases one-dimensionally and
continuously toward the periphery from the inverted peak value, or
toward the first phase region 1a and the second phase region.
[0049] Referring to FIG. 4, the light intensity distribution in the
middle portion M between adjacent two inverted peak pattern
portions R, which are formed in accordance with adjacent two
phase-shift sections 1c, exhibits an irregular swell (an undulate
distribution in which the light intensity repeatedly increases and
decreases). In this case, it is desirable to generate a crystal
nucleus in a position where the inclination of the inverted peak
pattern of the light intensity distribution is great (a position
indicated by reference numeral 11 where the light intensity is not
higher than a fixed value). If, however, there is a swell (a repeat
of projections and depressions) in the middle portion M as
described above, a crystal nucleus is likely to be generated in a
position of the swell where the light intensity is low (an
undesired position indicated by reference numeral 12).
[0050] Even though a crystal nucleus is generated in a desired
position, the lateral growth that starts from the crystal nucleus
to the periphery thereof will stop at a portion L of the boundary
between each of the inverted peak pattern portions R and the middle
portion M, where the light intensity decreases. In other words, the
lateral growth starting from the crystal nucleus will be limited to
the range of the width W of each of the inverted peak pattern
portions (the distance between the proximal ends of the inverted
peak pattern portions, or the distance between points or their
vicinities where the increasing light intensity starts to decrease
first). A considerably large crystal is therefore prevented from
growing. Incidentally, in the image defocus method, the width W of
each of the inverted peak pattern portions varies almost in
proportion to the {fraction (1/2)}th power of the distance between
the image surface of the image-forming optical system 3 and the
substrate 4 (i.e., amount of defocus) if the image-forming optical
system 3 has adequate resolution. On the other hand, in the image
NA method, the width W of each of the inverted peak pattern
portions is substantially equivalent to the resolution of the
image-forming optical system.
[0051] As described above, the KrF excimer laser light source 2a
supplies a laser beam whose oscillation wavelength band is
relatively broad unless the band is particularly narrowed. If the
image-forming optical system 3 is made of a single type of optical
material (e.g., silica glass), a relatively large chromatic
aberration occurs. In the present embodiment, an amount of
occurrence of a chromatic aberration (generally an amount of
occurrence of a wave aberration) of the image-forming optical
system 3 is defined in accordance with the oscillation wavelength
band of laser beams supplied from the KrF excimer laser light
source 2a. Therefore, no swell of light intensity occurs in the
middle portion, and the substrate (semiconductor film) 4 can be
irradiated with a laser beam whose light intensity distribution has
inverted peak pattern portions.
[0052] The principle of the present invention will be described
below with reference to a specific example of numeric values.
[0053] FIG. 5 is a graph showing an oscillation wavelength
distribution of the KrF excimer laser light source in the example
of numeric values according to the present embodiment. In this
graph, the horizontal axis indicates a position corresponding to
the length obtained by subtracting 248 nm from the wavelength
(unit: nm) and the vertical axis indicates the oscillation
intensity (relative value). As shown in FIG. 5, the laser beam
emitted from the KrF excimer laser light source 2a has a Gaussian
intensity distribution as a whole. More specifically, the central
wavelength .lambda. of the laser beam is 248.55 nm, and the full
width at half maximum of the oscillation wavelength distribution is
about 0.3 nm (full width at half maximum
.DELTA..lambda..apprxeq.0.15 nm).
[0054] In the example of numeric values according to the present
embodiment, the image-forming optical system 3 is made of only
silica glass and telecentric for both object and image sides at an
equal magnification. More specifically, the whole length of the
image-forming optical system 3 (the distance between the object
surface and the image surface) is 1000 mm (an 4f optical system:
f=250 mm), and the numerical aperture thereof on its laser beam
emitting side is 0.1. The illumination NA of the illumination
system 2 is 0.05. The pitch P between the phase-shift sections 1c
in the phase-shift mask 1, or the width of each of the phase
regions 1a and 1b is 10 .mu.m (see FIG. 3).
[0055] The displacement of an image-forming position due to the
chromatic aberration of the image-forming optical system 3 will now
be described with reference to FIGS. 6A and 6B.
[0056] When no chromatic aberration occurs in the image-forming
optical system 3, light beams emitted from one point on the optical
axis O of the phase-shift mask 1, which do not rely upon their
wavelengths, are focused through the image-forming optical system 3
upon one point on the optical axis O of the surface 4a of the
substrate 4 to thereby form a point image. In the present
embodiment, however, a chromatic aberration occurs in the
image-forming optical system 3. Therefore, as shown in FIG. 6A, of
the light beam emitted from one point on the optical axis O of the
phase-shift mask 1, a light beam 13 of a central wavelength is
focused upon the optical axis O on the surface 4a of the substrate
4, a light beam 14 of a wavelength shorter than the central
wavelength is focused upon the optical axis O above the surface 4a
of the substrate 4 (on the image-forming optical system side), and
a light beam 15 of a wavelength longer than the central wavelength
is focused upon the optical axis below the surface 4a of the
substrate 4 (on the opposite side of the image-forming optical
system). Consequently, in the present embodiment, the light beam
emitted from one point on the optical axis of the phase-shift mask
1 form an image, which is defocused to elongate along the optical
axis O as indicated by a hatched ellipse in FIG. 6B, on the surface
4a of the substrate 4. Since, moreover, the image-forming optical
system 3 is telecentric for both sides, the amounts of defocus in
all points on the flat surface 4a of the substrate 4 are almost
equal to each other, and the image is defocused in a direction
parallel to the optical axis. Paying attention to the points
corresponding to the respective wavelengths of images elongated in
the direction of the optical axis, or the points defocused from the
surface 4a of the substrate 4, the light intensity distribution
finally formed on the surface 4a of the substrate 4 is one obtained
by superimposing (synthesizing) light intensity patterns formed by
light fluxes of the respective wavelengths.
[0057] The following Table 1 shows a relationship between an amount
of wavelength displacement (nm) that is obtained by subtracting the
central wavelength .lambda. from the wavelength of each of the
light beams and an amount of longitudinal aberration (amount of
defocus: .mu.m) that occurs in each of the light beams due to the
chromatic aberration of the image-forming optical system 3 in the
example of numeric values according to the present embodiment. It
is seen from Table 1 that the amount of wavelength displacement and
the amount of longitudinal aberration are almost in proportion to
each other. The relationship shown in Table 1 is a result of
computations performed on the assumption that the image-forming
optical system 3 is a thin lens. This relationship is generally
established even in the actual image-forming optical system 3 that
is formed by a combination of a plurality of lenses.
1TABLE 1 Amount of 0.00 0.05 0.10 0.15 0.20 0.25 -0.05 -0.10 -0.15
-0.20 -0.25 Wavelength Displacement Amount of 0 19 39 58 77 97 -19
-39 -58 -77 -97 Longitudinal Aberration
[0058] FIG. 7 is a graph showing light intensity pattern formed on
the substrate by a light beams of respective wavelengths in the
example of numeric values according to the present embodiment. FIG.
8 is a graph showing a light intensity distribution finally formed
on the substrate 4 in association with the phase-shift mask in the
example of numeric values according to the present embodiment. In
FIG. 7, reference numeral 21 indicates a light beam (solid line)
whose wavelength coincides with the central wavelength .lambda.,
reference numeral 22 indicates a light beam (one-dot-one-dash line)
whose wavelength is displaced by .+-.0.05 nm from the central
wavelength .lambda., reference numeral 23 indicates a light beam
(broken line) whose wavelength is displaced by .+-.0.1 nm from the
central wavelength .lambda., reference numeral 24 indicates a light
beam (two-dot-one-dash line) whose wavelength is displaced by
.+-.0.15 nm from the central wavelength .lambda., reference numeral
25 indicates a light beam (chain line) whose wavelength is
displaced by .+-.0.2 nm from the central wavelength .lambda., and
reference numeral 26 indicates a light beam (three-dot-one-dash
line) whose wavelength is displaced by .+-.0.25 nm from the central
wavelength .lambda..
[0059] Referring to FIG. 7, a light intensity pattern formed by the
light beam 21 whose wavelength coincides with the central
wavelength .lambda. corresponds to the light intensity distribution
having inverted peak pattern portions and a middle portion shown in
FIG. 4. However, as the wavelength displaces from the central
wavelength .lambda., the minimum value of each of the inverted peak
pattern portions increases to some extent, but a degree to which
the light intensity suddenly decreases from each of the inverted
peak pattern portion toward the middle portion is lowered (the
level of normal peak patterns located both sides of each of the
inverted peak pattern portions is lowered. In the light beam whose
wavelength is displaced greater than a fixed distance, i.e., the
light beams 24 to 26 whose wavelengths are each displaced greater
than .+-.0.15 nm from the central wavelength .lambda., the light
intensity does not decrease from each of the inverted peak pattern
portions toward the middle portion (no normal peak patterns occur),
and almost no swell of light intensity occurs in the middle
portion.
[0060] As described above, the light intensity patterns formed by
light beams of respective wavelengths (i.e., the light intensity
patterns shown in FIG. 7) are superimposed to obtain a light
intensity distribution that is finally formed on the surface 4a of
the substrate 4. In the example of numeric values according to the
present embodiment, as shown in FIG. 8, the surface 4a of the
substrate 4 is irradiated with the light beam of a light intensity
pattern distribution having a normal peak pattern (angle pattern)
in which the light intensity has no swell in the middle portion M
between the inverted peak pattern portions R but increases slightly
and substantially monotonously toward the center of the middle
portion.
[0061] The term "mountain shape" used in the specification means a
pattern or shape of a mountain or triangular shape having not only
an angular top but also a sounded or non-angular top.
[0062] Consequently, any crystal nucleus can be generated not in
the middle portion M but in a position where the inclination of the
inverted peak pattern portions of the light intensity distribution
is great (or a position where the intensity is not higher than a
fixed value). Furthermore, the light intensity does not decrease in
the boundary between each of the inverted peak pattern portions R
and the middle portion M (no normal peak patterns L are formed),
but increases slightly and monotonously toward the center of the
middle portion M; therefore, the lateral growth starting from the
crystal nucleus toward its periphery is not limited to the range of
the width of each of the inverted peak pattern portions. Thus, in
the present embodiment, a crystal nucleus can be generated in a
desired position and a considerably lateral growth from the crystal
nucleus can be achieved to form a large-diameter crystallized
semiconductor film.
[0063] There now follows an explanation of conditional expressions
to obtain a light intensity distribution of patterns in which the
light intensity increases slightly and monotonously toward the
center of the middle portion M. The width W of an inverted peak
pattern portion formed when a longitudinal aberration due to the
chromatic aberration of the image-forming optical system 3 has a
maximum value D is given by the following expression (1) based on
the theory that is generally understood as a method of determining
a diffraction pattern of a Becke line.
W=2.times.1.2(.lambda..multidot.D/2).sup.1/2 (1)
[0064] where .lambda. is the central wavelength of a laser beam
supplied from the light source 2a.
[0065] Considering a process of the computation in the above
example of numeric values, it is desirable that the width W of each
of inverted peak pattern portions be substantially the same as the
pitch X between the inverted peak pattern portions (see FIG. 8) in
order to obtain a light intensity distribution of patterns in which
the light intensity increases slightly and monotonously toward the
center of the middle portion M. More specifically, the light
intensity pattern corresponding to the light beam 24 in FIG. 7 is
close to this condition. Considering that an adequate advantage is
obtained if the width W of each of inverted peak pattern portions
is somewhat close to the pitch X between the inverted peak pattern
portions, it is desirable that the following expression (2) be
established between the width W and the pitch X.
0.5.times.X.ltoreq.2.times.X (2)
[0066] A relationship between the pitch X between the inverted peak
pattern portions and the pitch P between the phase-shift sections
of the phase-shift mask 1 depends upon the image-forming
magnification of the image-forming optical system 3. In the example
of numeric values according to the present embodiment, the
image-forming magnification of the image-forming optical system 3
is equal magnification and thus the pitch X between the inverted
peak pattern portions coincides with the pitch P between the
phase-shift sections. Substituting the expression (1) for the
expression (2), the conditions of the following expression (3) are
derived, as are those of the following expression (4).
0.25X.sup.2/(2.times.1.44.lambda.).ltoreq.D.ltoreq.4X.sup.2/(2.times.1.44.-
lambda.) (3)
0.87.ltoreq.D.multidot..lambda./X.sup.2.ltoreq.1.389 (4)
[0067] Substituting X=10 .mu.m and .lambda.=0.24855 .mu.m for the
expression (4) as specific values of the example of numeric values,
the following conditional expression (5) is obtained with respect
to the maximum value D of the longitudinal aberration due to the
chromatic aberration of the image-forming optical system 3.
35 .mu.m.ltoreq.D.ltoreq.560 .mu.m (5)
[0068] Referring again to Table 1, it is understood that the
conditional expression (5) is satisfied even though an amount of
longitudinal aberration 97 .mu.m corresponding to the maximum
wavelength or the minimum wavelength is used as the maximum value D
of the longitudinal aberration or an amount of longitudinal
aberration 58 .mu.m corresponding to the half width is used. As
described above with reference to Table 1, the image-forming
optical system 3 with a chromatic aberration has a linear
relationship between an amount of displacement of a wavelength from
the central wavelength .lambda. and an amount of defocus (an amount
of longitudinal aberration). In other words, the maximum value D of
the longitudinal aberration corresponding to the half width can be
expressed by the following equation (6).
D=k.times..DELTA..lambda. (6)
[0069] where .DELTA..lambda. is a half width at half maximum in the
intensity distribution of the laser beam supplied from the light
source 2a, and k is a coefficient showing a ratio of the amount of
defocus to the amount of displacement of wavelength from the
central wavelength .lambda.. The conditional expression (4) can
thus be modified to the following conditional expression (7) with
reference to the relationship of the equation (6).
0.087.ltoreq.k.multidot..DELTA..lambda..multidot./X.sup.2.ltoreq.1.389
(7)
[0070] In the present embodiment, it is desirable to satisfy the
conditional expression (4) or (7) to obtain a light intensity
distribution of patterns in which the light intensity increases
slightly and monotonously toward the center of the middle portion.
In the foregoing embodiment, the KrF excimer laser light source 2a
supplies a laser beam having a Gaussian intensity distribution as a
whole. As a modification to this, however, the KrF excimer laser
light source 2a can supply a laser beam having a maximum intensity
at a plurality of given wavelengths that differ from one
another.
[0071] FIGS. 9A and 9B are illustrations of the structures and
functions of different etalons each of which converts a broadband
wavelength light beam into a plurality of light beams of different
wavelengths as modifications to the present embodiment. The etalon
shown in FIG. 9A is an air gap type etalon and that shown in FIG.
9B is a solid type etalon. FIGS. 10A and 10B are charts showing a
light source oscillation wavelength distribution and point images
formed by a plurality of wavelength light beams in the
modifications to the present embodiment. The etalon 28 shown in
FIG. 9A is made up of a pair of parallel flat plates 28a and 28b
arranged with a given gap t therebetween. These parallel flat
plates 28a and 28b are each formed of transparent glass. In the
etalon 28 so formed, a light beam that has passed through the first
flat plate 28a, e.g., a laser beam is applied to and/or reflected
by the incident surface of the second flat plate 28b and finally
emitted from the second flat plate 28b as light having a plurality
of optical elements whose wavelengths differ from each other. In
this case, a peak interval .delta..lambda. between a plurality of
(four in this embodiment) discrete wavelength light beams, which
are formed by the etalon 28 based on a broadband wavelength
incident laser beam, is represented by the following equation
(8).
.delta..lambda.=.lambda..sup.2/(2t cos .theta.) (8)
[0072] where .lambda. is the central wavelength of a broadband
wavelength light beam that is inherently supplied from the light
source 2a and its value is 248.5 nm in the present modification,
and .theta. is an incident angle of a laser beam to the etalon and
its value is 0 degree. To obtain a peak interval .delta..lambda. of
0.133 nm, for example, a given gap t has to be set to 231 .mu.m. In
other words, a light beam having four peak wavelengths whose peak
shapes are the same in the intensity distribution as shown in FIG.
10A can be obtained based on a broadband wavelength light beam
supplied from the light source 2a by the action of the etalon 28
with a gap t of 231 .mu.m.
[0073] The light beam having four peak wavelengths includes a first
wavelength optical component A1 whose central wavelength is 248.3
nm, a second wavelength optical component B1 whose central
wavelength is 248.433 nm, a third wavelength optical component B2
whose central wavelength is 248.566 nm, and a fourth wavelength
optical component A2 whose central wavelength is 248.7 nm. In this
case, as shown in FIG. 10B, the first wavelength optical component
A1 forms a point image C1, which is defocused due to a chromatic
aberration of the image-forming optical system 3, above the surface
4a of the substrate 4 (toward the image-forming optical system 3).
The second wavelength optical component B1 forms a defocused point
image D1 between the surface 4a of the substrate 4 and the point
image C1. Similarly, the third wavelength optical component B2
forms a defocused point image D2 in a position that is
diametrically opposed to the point image D1 with regard to the
surface 4a of the substrate to be processed. The fourth wavelength
optical component A2 forms a defocused point image C2 in a position
that is diametrically opposed to the point image C1 with regard to
the surface 4a of the substrate 4. The intervals of these point
images (C1, D1, D2, C2) are the same. The point images are included
in an elliptic region (indicated by hatching) corresponding to an
elliptic hatched portion indicative of a defocused image that is
elongated in the direction of the optical axis in FIG. 6.
[0074] In the present modification, too, the light intensity
distribution finally formed on the surface 4a of the substrate 4 is
one obtained by superimposing (synthesizing) light intensity
patterns formed by the wavelength optical components (A1, B1, B2,
A2).
[0075] It will be understood that the same advantage as that of the
above air gap type etalon can be obtained from another type of
etalon, e.g., a solid type etalon with a reflecting film 29a on
either side of a transparent flat substrate 29 having a thickness
of t as shown in FIG. 9B.
[0076] FIG. 11 is a graph showing a light intensity pattern formed
on the substrate by each of the four wavelength optical components
(A1, B1, B2, A2) described above.
[0077] Referring to FIG. 11, in the light intensity patterns formed
by the second and third wavelength optical components B1 and B2
whose wavelengths are each relatively close to the central
wavelength .lambda., the light intensity tends to decrease to some
extent from each of the inverted peak pattern portions toward the
middle portion therebetween. In contrast, in the light intensity
patters formed by the first and fourth wavelength optical
components A1 and A2 whose wavelengths are each distant from the
central wavelength .lambda., the minimum value of each of the
inverted peak pattern portions increases, whereas the light
intensity does not decrease from each of the inverted peak pattern
portions toward the middle portion therebetween or no swell of the
light intensity occurs in the middle portion.
[0078] FIG. 12 is a graph showing a light intensity distribution
obtained by synthesizing the optical components shown in FIG. 11
and finally formed on the substrate 4.
[0079] As shown in FIG. 12, a light intensity distribution in which
no swell of light intensity occurs in the middle portion M between
the inverted peak pattern portions R but the light intensity
increases monotonously toward the center of the middle portion M,
is finally formed on the surface 4a of the substrate 4. Thus, any
crystal nucleus is not generated in the middle portion M but can be
done in a position where the inclination of the inverted peak
pattern portions R in the light intensity distribution is great.
Since the light intensity increases monotonously toward the center
of the middle portion M more clearly than in the above-described
embodiment, the lateral crystal growth starting from a crystal
nucleus toward its periphery is easy to reach almost the central
part of the middle portion without being limited to the range of
the width of each of the inverted peak pattern portions.
[0080] In the present modification, too, a crystal nucleus can be
generated in a desired position and an adequate lateral crystal
growth from the crystal nucleus can be achieved to form a
large-diameter crystallized semiconductor film, as in the above
embodiment. In the present modification, the degree of freedom of
design for the shape and the number of peaks of each wavelength
light beam is higher than that in the above embodiment. It is thus
easier to achieve a light intensity distribution in which the light
intensity increases positively and monotonously toward the center
of the middle portion than in the above embodiment.
[0081] In the above modification, a broadband wavelength light beam
is converted into a plurality of wavelength light beams using an
etalon. However, the present invention is not limited to this. If a
plurality of laser beams that slightly vary in oscillation
wavelength are synthesized, a plurality of desired wavelength light
beams can be obtained using a plurality of light source sections
for supplying light beams whose central wavelengths generally
differ from one another and a synthesizing section for synthesizing
a plurality of laser beams supplied from the light source sections.
Instead, a plurality of desired wavelength light beams can be
obtained by inserting a multi-film mirror, which reflects only the
light beam of a specific wavelength, into an illumination optical
path of a broadband wavelength light beam. In this case, it is seen
from FIG. 7 that a great improvement can be provided simply by
eliminating only the central wavelength that contributes to a swell
of the intensity distribution the most.
[0082] The above embodiment employs the phase-shift mask 1 that is
formed by one-dimensionally arranging two types of slit-shaped
phase regions corresponding to phases 0 and .pi.. However, the
present invention is not limited to this, but a phase-shift mask
that is formed by two-dimensionally arranging four rectangular
regions corresponding to phases 0, .pi./2, .pi., and 3.pi./2 can be
used. Furthermore, in general, a phase-shift mask having an
intersection point (phase shift section) of three or more phase
shift lines and formed such that the integral of the complex
transmittance of a circular region with the intersection point at
the center can be used. Moreover, a phase-shift mask having a
circular step corresponding to a phase-shift section and set such
that a phase difference between a transmitted light beam of the
circular step and its surrounding transmitted light beam becomes
.pi. can be used. The light intensity distribution can be computed
even in the design stage, but it is desirable to observe and
confirm the light intensity distribution on the actual surface to
be processed (the surface to be exposed). To do this, the surface
to be processed has only to be expanded by an optical system to
receive a light beam through an image pickup device such as a CCD.
When a light beam for use is ultraviolet rays, the optical system
subjects to constraints and thus the light beam can be converted to
a visible one by providing a fluorescent plate on the surface to be
processed.
[0083] A method of manufacturing an electronic device by the
manufacturing device and method of the present invention will be
described with reference to FIGS. 13A to 13E.
[0084] As illustrated in FIG. 13A, an underlayer film 31 (e.g., a
laminated film of an SiN film having a thickness of 50 nm and an
SiO.sub.2 film having a thickness of 100 nm) and an amorphous
semiconductor film 32 (e.g., Si, Ge and SiGe each having a
thickness of about 50 nm to 200 nm) are formed all over a
rectangular insulation substrate 30 (e.g., alkaline glass, silica
glass, plastic, and polyimide) by chemical vapor deposition,
sputtering and the like. Then, an excimer laser beam 33 (e.g., KrF
and XeC1) is applied to part or all of the surface of the amorphous
semiconductor film 32. To apply the excimer laser beam, the device
and method of the above embodiment are used. Consequently, the
amorphous semiconductor film 32 is crystallized into a
polycrystalline semiconductor film 34 as shown in FIG. 13B. The
polycrystalline semiconductor film 34 so formed is converted to a
polycrystallized or single crystallized semiconductor film whose
crystal grain positions are controlled and whose crystal grain
diameter is larger than that of a polycrystalline semiconductor
film formed by the conventional manufacturing device.
[0085] The polycrystallized semiconductor film 34 is processed by
photolithography to form island-like semiconductor films 35. As
shown in FIG. 13C, an SiO.sub.2 film having a thickness of 20 nm to
100 nm is formed on the underlayer film 31 and semiconductor film
35 as a gate insulation film 36 by chemical vapor deposition,
sputtering or the like.
[0086] Then, a gate electrode 37 (e.g., silicide and MoW) is formed
in a location corresponding to the semiconductor film 35 on the
gate film 36. Using the gate electrode 37 as a mask, impurity ions
38 (phosphorus is used when the device is an N-channel transistor,
and boron is used when it is a P-channel transistor) are implanted
into the semiconductor film 35 to make this film an N type or a P
type. After that, the entire device is annealed in a nitrogen
atmosphere (e.g., for one hour at 450.degree.) to activate the
impurities in the semiconductor film 35. As a result, the
semiconductor film 35 serves as a source 41 and a drain 42 both
having a high impurity concentration, and a channel region 40
located therebetween, corresponds to the gate electrode 37 and
having a low impurity concentration.
[0087] An interlayer insulation film 39 is formed on the gate film
36. Then, contact holes are formed in those portions of the
interlayer insulation film 39 and gate film 36 that correspond to
the source 41 and drain 42. After that, a source electrode 43 and a
drain electrode 44, which are electrically connected to the source
41 and drain 42 through the contact holes, are formed on the
interlayer insulation film 39 by deposition and patterning, as
shown in FIG. 13E. It can be understood that the thin-film
transistor so formed is a large-diameter polycrystal or monocrystal
since a semiconductor that forms the channel 40 is processed by
laser beam irradiation as described with reference to FIGS. 13A and
13B. The switching speed of such a transistor is higher than that
of a transistor using an amorphous semiconductor to which no laser
beam is applied. A polycrystallized or single crystallized
transistor can be designed to have a liquid crystal driving
function and a function of integrated circuits such as a memory
(SRAM, DRAM) and a CPU. A circuit that requires a withstanding
voltage is formed in an amorphous semiconductor film, while a
transistor of a driver circuit that requires high-speed mobility is
polycrystallized or monocrystallized.
[0088] As described above, according to the present invention, an
inverted peak pattern light intensity distribution is formed on the
substrate to be processed, in which the light intensity does not
decrease in the boundary between each of the inverted peak pattern
portions and the middle portion therebetween but increases
monotonously toward the center of the middle portion through a
cooperation between a light source for supplying light beams within
a given range of wavelengths and an image-forming optical system
having an aberration corresponding to the range of wavelengths.
Consequently, a crystal nucleus can be generated in a desired
position and an adequate lateral growth from the crystal nucleus
can be achieved to form a large-diameter crystallized semiconductor
film.
[0089] In the above descriptions, a subject to be crystallized is
regarded as a substrate to be processed. It will be understood that
the subject to be processed is an amorphous and polycrystalline
layer or film formed on the substrate, as described in the above
embodiment. To crystallize a substrate in itself is also included
in the present invention and, in this case, the substrate serves as
a subject to be processed. The material to be crystallized is not
limited to silicon. For example, another semiconductor such as Ge
and SiGe can be used. The material is not limited to a
semiconductor but has only to be metal if it has crystallinity. In
the present invention, crystallization means improving a degree of
crystallization. For example, the crystallization of an amorphous
matter means that it is converted to a polycrystalline or image
crystal matter, and that of a polycrystalline matter means that it
is converted to a image crystal matter.
[0090] In the present invention, the phase-shift section of the
phase-shift mask is not limited to a boundary or a point between
different phase regions, but includes a nearby portion of the
boundary and point. For example, when a light-shield region that
extends along the boundary of the phase-shift mask is provided in
one of adjacent phase regions, the light-shield region is a
phase-shift section. In other words, an inverted peak pattern
portion having a peak value of the minimum strength is formed to
correspond to the light-shield region.
* * * * *